I made the discovery a few seasons ago that there are conditions where a polished shell just will not provide the best ball reaction on certain lane conditions.  I know that sounds simple but for me it was not.  I used to think that as long as I was able to get the ball to react enough to get to the pocket on a given delivery, there was no need to change the shell.  I was so wrong!  

When I began to adjust the surfaces of my bowling balls, I became a more complete bowler and my scores reflected that.  I began to use Scotch brite pads as well as wet/dry sand paper to adjust shells from semi-rough (burgandy pad) to very smooth.(1500 grit-no polish) I also would adjust the shell on the ball paying close attention to the direction of the sanding in relation to my ball track.  

The point is, don't let yourself get into that habbit of polishing every ball you own!  You won't believe how nicely a ball without polish will react for you, it doesn't have to be super dull.  Try 800, 1000, 1200 or even 1500 grit wet sanding without polish.  I used to worry that I needed the polsih because I didn't throw hard enough to use a dull ball, also not true.  Try it once and you will wonder why you waited!